docs: def convert_date(obj):
      """Returns a DATE column as a date object:
  
        >>> date_or_None('2007-02-26')
        datetime.date(2007, 2, 26)
  
      Illegal values are returned as None:
  
        >>> date_or_None('2007-02-31') is None
        True
        >>> date_or_None('0000-00-00') is None
        True
  
      """
      try:
          return datetime.date(*[ int(x) for x in obj.split('-', 2) ])
      except ValueError:
          return None